Mobile terminals provided with a capacitive touchpad unit have been conventionally suggested (see Patent Literature 1). The suggested capacitive touchpad unit measures a change in the capacitance of the touchpad unit at a position corresponding to each key of the touchpad unit to determine whether the key is being touched based on the measurement values.
The measurement values are sensitive to the temperature change in the touchpad unit. Therefore, the measurement values need to be corrected (calibrated) to remove the influence of the temperature change in order to accurately detect a key touch.
In addition, the temperature of the touchpad unit varies from time to time depending on various factors, including the use environment. Therefore, the calibration coefficient used for calibration of measurement values needs to be updated regularly. In addition, the update of the calibration coefficient needs to be carried out in the state where the touchpad unit is not in contact with an operating member in order to eliminate the influencing factors other than the temperature as much as possible.
In view of the above, one conventionally suggested mobile terminal regularly updates the calibration coefficient (updates the reference capacitance value) using a value measured for a key selected from the touchpad keys not in contact with an operating member (see Patent Literature 2).